1. Field of the Invention
The present invention relates to the field of radio telecommunication apparatuses used in a radio telecommunication system such as a motor vehicle radio telephone system and a portable radio telephone system and, more particularly, to a radio telecommunication apparatus able to display whether the apparatus is located in its service area.
2. Description of the Related Art
A cellular radio communication system will be described with reference to FIG. 11. The system comprises control station CS connected with wire telephone network NW, a plurality of base stations BS1-BSn, which are respectively connected with control station CS via landlines CL1-CLn, and a plurality of mobile radio apparatuses MS1-MSn. Each of these base stations BS1-Bsn has its own radio zone E1-En, respectively. The mobile radio apparatuses MS1-Msn may be in communication with the base stations BS1-Bsn via radio links in the radio zones E1-En. If an apparatus user travels out of zone E1 and enters another zone E2, a radio link is established between the apparatus and base station BS2 instead of between the apparatus and base station BS1.
A plurality of zones (E1-En) provides a service area. Furthermore, a plurality of service areas are provided in a cellular radio system. Each of the service areas is controlled by its respective control station. If an identification number of the apparatus is registered in a control station, the service area is called a home area. Otherwise, the area is called a roam area.
User fees for calls from the cellular radio telephone apparatus in a roam area are higher than the fees in a home area. When a calling party is located in a roam area and originates a call, a high fee is usually charged for the communication.
Further, when a party is called and receives an incoming signal while located in a roam area, a high fee is charged for the communication.
Still further, each of the roam areas are serviced by different service companies. Therefore, user fees for calls from an apparatus in one roam area are different from those in another roam area.
In order to reduce user fees, users normally do not wish to communicate with a "high charge" service area. However, when the calling party is located in the "high charge" service area and originates a call, the conventional radio telecommunication apparatus is obliged to be connected with that system. Further, when the called party is located in the "high charge" service area and receives an incoming signal, the conventional apparatus is obliged to be connected with that system.